The invention is directed to an asynchronous interface for use with keyed electronic musical instruments. In particular, the invention is directed to an asynchronous interface for electronically simulating or synthesizing the key contact closures of an electronic musical instrument having a keyboard multiplexer which digitally multiplexes key contact closures into a serial time signal, each key being represented by a unique time slot within the multiplexed signal. The invention is applicable to any musical instrument utilizing multiplexed notes and/or voice selection. It can be used in a sequencer, automatic player, automatic chord generator, automatic accompaniment player, multiple organ system (for keying the organs from a single group of contacts), voice selection circuits, and the like.
The keyboards and stop tabs of modern musical instruments are the product of centuries of adaptation to the human controlling mechanism (fingers, hands, feet). As such, the instruments perform excellently under the player's guidance.
It is often desirable, however, that some mechanical, electrical, or electronic system replace or augment the player's performance. Such systems are exemplified by the player piano, sequencers and the many automatic chord generators known in the electronic musical instrument field.
Early mechanized musical instrument controllers relied on rather complex mechanical or pneumatic hardware to physically depress the instrument keys to simulate a player's performance. The best known example of such a system is the player piano. Such systems are characterized by relatively cumbersome, expensive, and failure prone mechanical hardware. Later electrified controllers provided solenoids which also physically depressed the instrument keys (or operated the key relays). Although an improvement, such controllers were also burdened by rather cumbersome, expensive, and unreliable components.
The advent of electronic musical instruments having multiplexed systems for selection of notes and voices, as in the Allen digital computer organ, enables the use of improved electronic controllers for the musical instrument. By multiplexing key closure information to a single multiplexed data stream, it is unnecessary tor the controller to separately access each key. Instead, the controller can tap into the multiplexed keyboard data stream. Many performer augmentation devices such as automatic chord and bass generating systems have since been described and introduced for use with such multiplexed systems. Typically, these devices analyze key depressions made by the performer and generate complementary chords and bass notes by introducing additional keying information into the multiplexed data stream of the instrument.
U.S. Pat. Nos. 4,129,055 and 3,889,568 disclose various performer augmentation devices for use with an electronic musical instrument. U.S. Pat. No. 4,129,055 discloses a chord accompaniment circuit wherein, in a playback mode, data is transferred from a chord memory 44 to a chord generator 38. The chord data (based on key depressions) is written into a memory 52 in the program mode and is read out of the memory 52 in the playback mode. In U.S. Pat. No. 3,889,568, the chord data is stored in a RAM 3, and data is read out of the RAM by a pair of address circuits 5, 6 under control of a clock 7.
The use of various memory devices is also known in the electronic musical instrument field. For example, U.S. Pat. No. 3,894,463 discloses a tone generator wherein sampled (waveform) data from an A/D converter 15 is written into a RAM 16 at a relatively slow rate set by a clock 3. Data is read from the RAM at a higher rate set by a clock 23. Each read operation entails reading out all data in the RAM i.e., all waveform sample points, and takes place between successive write operations. Each write operation entails writing a single sample point of waveform data into the memory. U.S. Pat. No. 4,078,465 discloses a programmable memory wherein bi-directional transfer of data takes place between an input system 40 (keyboard), RAM 22 and EPROM 10; and between EPROM 10 and the musical instrument. Control of the data transfer is exercised by a data transfer control 64.
As the selection of notes and voices by means of keyboard multiplexing becomes more common due to advances in electronics technology, attention is focused on the design of systems having multiple musical instruments, remote keying systems, computer control systems, and digital sequencers. Such systems can be realized by an an interfacing device which can accept a standard input and produce as its output a multiplexed keying signal that is compatible with the signals and data normally generated by the musical instrument or instruments.